The invention relates to an optical coupling device for injecting light between two optical waveguide end faces, it being possible to vary the geometrical position of the one optical waveguide end face, for example an optical fibre, with respect to the other optical waveguide end face, for example an optical waveguide chip, with the aid of a variable-length element which, via a holding device, carries one of the two optical waveguides and is fixed to the other optical waveguide by two holding blocks.
An optical coupling device is known, for example, from WO 98/13718. Such coupling devices are used in optical filters according to the phased-array principle with an injection face which light enters at a specific geometrical position, the geometrical position influencing the output wavelength of the optical filter. Such optical filters according to the phased-array principle are used, in particular, as multiplexers or demultiplexers in optical wavelength-multiplex operation (WDM), since they exhibit low insertion attenuation and high crosstalk suppression. The optical filter has, as an essential component, a plurality of curved optical waveguides of different length, which form a phase-shifter region.
German Patent Application DE 44 22 651.9 describes that the central wavelength of a phased-array filter can be established through the position of an injection optical waveguide, which guides the light into the optical waveguide. In this way, the central wavelength of the optical filter can be adjusted accurately through the geometrical positioning of the injection optical waveguide or the injection fibre. Since it is therefore desirable for the optical waveguides to be shifted relative to one another, the optical waveguides cannot be adhesively bonded directly to one another.
In the optical coupling device cited in the Field Of The Invention, the holding blocks are fixed to the chip, and the optical waveguide fibres are held on the variable-length element. In this case, the variable-length element may oscillate or bend, which causes temporary or permanent deadjustment of the fibre, even though a certain degree of guidance is provided.
The invention is, therefore, directed to ensuring improved guidance of the variable-length element parallel to its main extension direction (longitudinal axis of the element) and to avoid deadjustment during operation.
In the optical coupling device of the invention, the variable-length element or the holding element is held by a spring element, which is supported directly or indirectly on at least one of the holding blocks and permits movements of the variable-length element or the holding element in the longitudinal direction of the variable-length element in which the variable-length element extends or shortens, and suppresses movement of the variable-length element perpendicular to the longitudinal direction of the variable-length element, the spring element being held close to the fixing of the holding blocks on the other optical waveguide. In the invention, one optical waveguide, that is to say the optical fibre, is held as close to the fixing as possible by the spring element. The variable-length element, which is necessarily fixed, further removed, to the other (second) optical waveguide, that is to say to the chip, presses against the holding element for the fibre, in order to permit the relative movement of the fibre with respect to the chip. The spring element is configured in such a way that a residual movement perpendicular to the plane is suppressed as completely as possible. This means that the movement of the fibre relative to the chip takes place very exactly parallel to the chip face, and deadjustment perpendicular to the latter virtually does not occur.
In the invention, it is further advantageous that the holding block can be adhesively bonded to the second optical waveguide (optical waveguide chip, also called a planar waveguide) very close to the fibre, which avoids long levers. As a result, undesired movements in the directions perpendicular to the desired extension of the variable-length element are reduced considerably.
One advantageous configuration of the coupling device according to the invention is that the variable-length element, the holding element and the spring element are arranged between the two holding blocks, and in that the holding element is formed in one piece with the variable-length element, and the spring element is formed separately therefrom. In this case, it is advantageous that the material of the spring element can be selected without having to take into account the requirements which are placed on the material of the variable-length element.
A further advantageous configuration of the coupling device according to the invention is that the variable-length element, the holding element and the spring element are arranged between the two holding blocks, and in that the holding element, the variable-length element and the spring element are formed in one piece. This configuration has production advantages and also has advantages in relation to the operational reliability and the lifetime of the arrangement.
A further advantageous configuration of the coupling device according to the invention is that the variable-length element, the holding element and the spring element are arranged between the two holding blocks, and in that the holding element and the spring element are formed in one piece and the variable-length element is formed separately therefrom. Here, too, the holding elements and the spring element can be produced without any regard to the material of the variable-length element.
A further advantageous configuration of the coupling device according to the invention is that the spring element is formed by slots in the variable-length element or the holding element, the said slots lying in a plane parallel to the end faces and perpendicular to the longitudinal direction of the variable-length element. These slots can be applied particularly advantageously when the variable-length element, the holding element and the spring element or, alternatively, at least the holding element and the spring element, are formed in one piece with one another. In addition, the direction of the slots is advantageous in as much as if the slots are rotated, for example through 90xc2x0, the stability in the critical direction perpendicular to the plane of the chip is no longer adequately guaranteed.
A further advantageous configuration of the coupling device according to the invention is that an even number of slots is provided. As a result, the tendency to tilt can be minimized.
A further advantageous configuration of the device according to the invention is that the spring element is formed by holes in the variable-length element or the holding element, the said holes lying in a plane parallel to the end faces and perpendicular to the longitudinal direction of the variable-length element. Holes of this type can easily be produced by machine, the spring constant of the spring element being adjustable via the size of the holes.
A further advantageous configuration of the coupling device according to the invention is that the spring element consists of bent spring sheet, whose spring sections lie in planes which are perpendicular to a plane which is perpendicular to the chip face and perpendicular to the longitudinal direction of the variable-length element. This orientation of the spring sections is advantageous with regard to suppressing the oscillatory movements perpendicular to the longitudinal direction of the variable-length element.
A further advantageous configuration of the coupling device according to the invention is characterized in that the length of the variable-length element is selected such that the spring element is under pre-stress in the initial position of the variable-length element. This ensures that the holding device, if it is formed separately from the variable-length element, follows the variable-length element when the latter contracts.
A further advantageous configuration of the device according to the invention is that the two holding blocks are connected to each other by a clip, the arrangement, comprising the two holding blocks, the variable-length element, the holding element and the spring element, being imparted greater stability.
A further advantageous configuration of the coupling device according to the invention is that the two holding blocks are connected to each other by a frame, a clip being provided at the top and bottom in each case between the two holding blocks, and the clips being produced from one piece with the holding blocks, so that they can be adhesively bonded to the chip together with the said holding blocks.
A further advantageous configuration of the coupling device according to the invention is that the spring element is located between the clip and the frame and the holding element which is located between the two holding blocks, and in that the variable-length element is mounted in one of the holding blocks and is connected to the holding element device. In this case, the bonding or fixing points of the entire arrangement, namely the adhesive bonding of the holding blocks to the chip, are located in the immediate vicinity of the injection point, and the relative movement between the two optical waveguides is carried out by means of the variable-length element, which is mounted in one of the holding blocks and presses against the holding element.
A further advantageous configuration of the coupling device according to the invention is that an opposing spring is provided between the holding element and the other holding block and, in the initial position of the variable element, is under pre-stress, by which means, in the event of contraction of the variable-length element, the corresponding return movement is increased.
A further advantageous configuration of the coupling device according to the invention is that the variable-length element is guided in one of the holding blocks and is operatively connected to a wavelength compensating screw, with which the position of the variable-length element can be adjusted in the longitudinal direction of the latter, as a result of which the zero position of the wavelength can advantageously still be adjusted, even after the coupling device has been bonded adhesively to the optical waveguide chip, which further increases the production reliability.
Finally, a further advantageous configuration of the coupling device according to the invention is that the holding element has a ferrule, in which the optical waveguide or the optical fibre is fixed. Although it would also be possible to fix the fibre to the spring element without a ferrule, for example by means of adhesive bonding in a V groove, the use of a ferrule is preferred because of the accuracy of the installation and the avoidance of ageing phenomena on the adhesive for the adhesive bonding of the fibre in the V groove.